Debating A and E

Hi, I debated A and E because I could make an argument that both of them were right. In situations like this I am not sure how to figure out which one to choose, do you have any advice? A: There has been a significant increase over the last 25 years in the proportion of individuals in households with more than one wage earner. Here I thought that if the individuals are spending the same proportion of their income in buying the car, but also getting some money from a wife or family member, that would weaken the argument that individuals are spending a higher proportion of their income on cars. I realize this argument requires an assumption not stated in the answer choice, but assumptions are a tricky topic because I find that in the harder questions, there seems to be room for some assumptions. E: Sales to individuals make up a smaller proportion of all new–car sales than they did 25 years ago. I also thought this was right for the reasons stated in the explanation. Other entities could be buying expensive cars, which could. be increasing the average while keeping individual proportions the same. But doesn't this also require the assumption that the other entities are spending a lot of money on cars? So how should I have decided between the two and in the future what is the best way to go about it